Abstract
In this study, a dynamic stall control strategy, called the co-flow jet (CFJ), is applied to the rotor airfoil. The effect of the CFJ on the unsteady dynamic stall characteristics of the rotor airfoil is numerically investigated via numerical simulations of the unsteady Reynolds-averaged Navier-Stokes (URANS) equations coupled with the Spalart-Allmaras (S-A) turbulence model. The numerical methods are validated by a NACA0012 pitching airfoil case and a NACA6415 airfoil case based on the CFJ, and good agreement with experiments is found. Via the study of the typical conditions of CFJ control to suppress the dynamic stall of the OA212 rotor airfoil, it is verified that this method has a good effect on dynamic stall suppression. The diffusion and blending of the turbulent shear layer between the CFJ injection jet and the main flow excite the main flow and enhance its ability to resist the reverse pressure gradient; this suppresses the generation and development of the separation vortex, thereby enhancing the aerodynamic characteristics, improving the hysteresis effect, and increasing the system stability. On this basis, the control parameters of the CFJ are further studied, including the influences of the jet momentum coefficient and the positions and sizes of the injection and suction slots on suppressing the dynamic stall of the rotor airfoil. It is found that there is a jet momentum coefficient that optimizes the suppression effect of the dynamic stall of the rotor airfoil. Moreover, the position of the injection slot is found to have a greater effect on the dynamic stall suppression, while the size of the injection slot and the position and size of the suction slot have little effect.
Highlights
As compared with a fixed-wing aircraft, helicopters have unique advantages, such as vertical take-off and landing, high maneuverability, and hovering in the air, and they are widely used in both military and civilian fields
The sliding mesh technique was used to solve the unsteady Reynolds-averaged Navier-Stokes equations, and the dynamic stall characteristics of the OA212 rotor airfoil based on co-flow jet (CFJ) control were numerically simulated
(1) Numerical simulations of a NACA0012 airfoil dynamic stall case and NACA6415 airfoil flow separation suppression case based on CFJ verified the correctness of the numerical simulation methods for airfoil dynamic stall and CFJ control
Summary
As compared with a fixed-wing aircraft, helicopters have unique advantages, such as vertical take-off and landing, high maneuverability, and hovering in the air, and they are widely used in both military and civilian fields. The dynamic stall leads to sharp increases in the drag coefficient and moment coefficient of the rotor blades, which seriously restricts the improvement of the aerodynamic performance and forward flight speed of helicopters. Active trailing-edge flaps and dynamic-droop leading edges tend to cause obvious changes to the center of gravity and load [32] They always require a complex mechanical adjustment mechanism and control systems. The effects of the control parameters of the CFJ on suppressing the dynamic stall of the rotor airfoil are investigated and include the jet momentum coefficient and the position and size of the injection and suction slots; the findings lay a foundation for the research on the dynamic stall control of actual rotor blades
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